Optical image recording system, and associated processing system

ABSTRACT

An optical image recording system for electronic recording of optical information comprising a lens system and a body The body having a configuration with a low height and with broad surfaces through one of which surfaces said optical information is being received, and accommodating an image recording device having a light sensitive area. The lens system includes a front lens group having a first optical axis, a back lens group consisting of one or more lenses having a second optical axis and a reflective element folding the first optical axis into the second optical axis in an angle of less than 180 degrees. The lens system is accommodated in the body; and an optical image recording and processing system for the recording and processing of electrical signals of optical information and other information.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 09/213,434,now U.S. Pat. No. 6,850,279, filed Dec. 17, 1998.

BACKGROUND OF THE INVENTION

The present invention relates to an optical image recording system andan associated processing system.

The Technical Field

Optical image recording systems such as conventional cameras andelectronic cameras are available in many different designs and sizes.

Portable cameras are usually miniaturized for the purpose of beingportable in a bag or pocket. A general problem of such portable camerasis that their sizes and shapes make them unpractical and unhandy tocarry along as can be done with personal equipment of sizes such as acredit card or drivers licence.

Electronic cameras are also available in different designs for variousapplications such as built-in cameras in permanent installations or asportable cameras. Such electronic cameras are usually designed on one ormore printed circuit boards (PCB) for which a minimum dimension in thetwo directions of the plane is required. The height of the camera isusually dependent on the dimensions of the lens system used, and it istotally dependant on the focal length thereof.

A disadvantage of these image recording systems is that they aredifficult to miniaturize.

Prior art lens systems for such cameras are often miniaturized by theuse of a limited number of lenses so that the effective lens heightthereof can be brought down to approximately 1 times the focal length ofthe lens system.

A consequence of using only a few, typically only one lens, is that theformed image has an unsatisfactory resolution and performance.Therefore, in order to achieve a reasonable resolution, it is necessaryto reduce the aperture whereby, however, the photosensitivity isreduced.

Further, if a low height is to be maintained, only a short focallength—and consequently a wide angle field of view—can be used. Anyincrease in the focal length of the lens will lead to an increase of theheight.

Especially for electronic cameras a further disadvantage is that thetransfer of the recorded optical information requires the use ofcumbersome external cables connecting the camera and image processingsystem, or it requires an exchangeable memory such as a diskette or asolid state memory. For the latter two data carriers, the cumbersomecables can be avoided, but they will require the software forcontrolling the image processing system to be loaded on the data carrierwhich requires space thereon.

Prior Art

JP 01-176 168 discloses a compact electronic still camera comprising acamera main body in form of a plastic resin card having a thicknesswithin 10 mm. The card camera comprises a CCD 2-dimensional image sensorand a semiconductor memory for electronic recording of an image, and aconnector for the connection of the circuit inside the card camera withthe circuit of an image reproducing device for transferring the stillpicture information thereto. The camera is provided with a demountablelens to be removed when the card camera must be flat.

DE 26 59 729 discloses a single lens reflex pocket camera having a twice90 degrees broken optical axis to accommodate a built in zoom lens. Thecamera receives the optical information through a side of the camerabody. Such a system has the disadvantage that when the body height islow, the viewfinder is not properly framed, i.e. it is difficult to lookthrough it and see the object. For a camera with a very low body height,it is impossible to look through the viewfinder. Furthermore, a downscaling of the disclosed optical system requires very small and thinlenses which are very difficult to manufacture within small toleranceswith present technology and which are impractical to handle. For animage recording system that should be mounted flat on a wall, e.g. aspart of a door phone, it cannot be allowed that the optical informationis received through a side of the camera body.

DE 25 53 395 discloses an endoscope objective comprising an invertedtelephoto objective connected to a waveguide. The endoscope neithercomprises a body having a configuration with a low height and with broadsurfaces, nor does it comprise an optical image recording system withimage recording device, viewfinder, and a solid state memory. Theendoscope objective cannot be accommodated in the body of an imagerecording system having an S-ratio less than 1.9, i.e. having a largediagonal of the image recording device as compared to the height of thebody of the image recording system, nor can a high resolution imagerecording system based on the endoscope objective be incorporated insuch a body having a size to be kept in a wallet or in the form of atype II PCMCIA card.

JP 63-199 312 discloses an electronic camera intended for small imagesizes and short focal lengths. The camera uses a non-folded lens systemhaving a long back focus allowing space for a blur filter to beincorporated therein. Very thin lenses are required, which is notdesirable from a practical point of view as the lenses become veryvulnerable and sensitive to variations in lens thickness. It isimpossible to effectively minimize the effective lens height. Hence, avery compact high resolution camera cannot be made.

EP 0 676 663 discloses a compact camera which is suitable for use ashidden or candid camera. The lens section is fabricated to minimize thethickness of the camera. In an embodiment, the camera includes a planebody having a pinhole disposed therein and a lens disposed on the planebody. Only short focal lengths can be accepted in order to maintain aflat body. The lens is a single element aspherical lens which results ina low resolution and limited speed which is not acceptable for highresolution applications. Furthermore, the back focus is too short toprovide enough space for colour filters comprising multiple birefringentplates to be inserted between the lens and the CCD. Hence, for highresolution applications aliasing might occur.

DISCLOSURE OF THE INVENTION

Optical Image Recording System

In a first aspect of the present invention, it is the object to providean optical image recording system for the recording of opticalinformation which system can be accommodated in a compact, flatconfiguration; particularly in a compact, flat camera which can be keptin a wallet or a small handbag designed for carrying credit cards.

It is a further object of the present invention to provide such anoptical image recording system for which the speed and resolution of theoptical information is substantially maintained as compared to prior artminiature, compact multiple lens systems.

It is another object of the present invention to provide such an opticalimage recording system which can comprise a birefringent blur filter,preferably a filter incorporating more than one birefringent quartzplate.

It is still another object of the present invention to provide such animage recording system which is less sensitive to variations in lensthickness.

According to the invention, these objects are fulfilled by providing anoptical image recording system for electronic recording of opticalinformation comprising a lens system and a body; said body having aconfiguration with a low height and with broad surfaces through one ofwhich surfaces said optical information is being received, andaccommodating an image recording device having a light sensitive area;which system is characterized in that the lens system comprises: a frontlens group having a first optical axis; a back lens group consisting ofone or more lenses having a second optical axis; and a reflectiveelement folding the first optical axis into the second optical axis inan angle a of less than 180 degrees; and that said lens system isaccommodated in said body whereby it is ensured that the optical imagerecording system achieves a compact, flat configuration.

Particularly, the optical image recording system can be embodied in acompact, flat camera which can be kept in a wallet or a small handbagdesigned for carrying credit cards. Such a camera has the advantagecompared to prior art cameras, e.g. card type cameras, that the lenssystem does not have to be removed from the body before being insertedinto such a wallet or handbag.

It is a further advantage that the focal length of the lens system canbe long. Contrary to this, the focal length of the prior art techniqueshas to be short in order to allow for a short objective which does notprotrude too far from the body surface.

Also, it is an advantage that the lens system can comprise opticalfilters, e.g. blur filters, particularly for high resolution electroniccameras.

The Lens System

According to the invention, the lens system comprises a front lens grouphaving a first optical axis; a back lens group consisting of one or morelenses having a second optical axis; and a reflective element foldingthe first optical axis into the second optical axis in an angle a ofless than 180 degrees, whereby it is obtained that the lens system canbe accommodated inside the body so that the effective lens height can bekept smaller than that for non-folded lens systems of the prior artcompact, flat cameras.

Further, it is achieved that the optical information received throughone of said broad surfaces of the body is received by the lens systemand transferred to the image recording device while maintaining speedand resolution.

The front lens group and the back lens group can be negative and/orpositive, respectively.

In a preferred embodiment, the front lens group is negative and the backlens group is positive whereby an inverted telephoto lens can berealized.

In another preferred embodiment, the front lens group is positive andthe back lens group is negative whereby a telephoto lens can berealized.

Front Lens Group

The front lens group may consist of one or more lenses.

Also, in a special case of a small field angle of view and a focallength long enough for the reflective element to receive the extremerays entering the system, the lens group may consist of a window.

The front lens group can be designed as known to a person skilled in theart. The desired field angle of view is the determining factor for theshape and complexity of the front lens group. For a wide angle field ofview, the front lens group is negative and together with the back lensgroup it forms an inverted telephoto lens system. Such a system has theadvantage that it can be designed to allow space between the front lensgroup and the back lens group for a reflective element. For aparticularly flat design of the body, the diameter of the last surfacein the front lens group should be minimized, thereby allowing the sizeof the reflective element to be minimized. For wide and medium anglefields of view, the diameter and complexity of the front lens group canbe reduced by reducing the field angle of view.

A reduction of the field angle of view allows the number of lenses inthe front lens group to be reduced because a smaller field of viewexhibits less aberrations whereby the lens height can be furtherreduced.

Also, a reduction of the speed of the lens system and/or an increase ofthe focal length, allow the diameter of the first lens group to bereduced and thereby allow a reduction of the lens height.

In a particular embodiment the front lens group is made stronglyrefractive, thereby allowing a small diameter of the last surface of thefront lens group and a small size of the reflective element. This,however, introduces a large geometric distortion which is not desiredfor a high quality lens system. However, by using a solid state imagesensor as the image recording device, the geometric distortion of thesystem can be electronically corrected. The front lens group maycomprise a gradient index (GRIN) lens, particularly a radical gradientindex lens whereby the lens height can be reduced or a higher qualityimage can be obtained.

Aspherical lenses can be used as well.

The front lens group may be positive or negative. In a preferredembodiment, the front lens group consists of a single negative lens.

Back Lens Group

According to the invention, the lens system comprises a back lens groupconsisting of one or more lenses having a second optical axis; said lensor lenses bending the incoming light by refraction, diffraction or acombination thereof whereby it is obtained that the optical informationreflected by the reflective element is formed into an image.

The number of lenses and their designs are chosen so that a sharp imagecan be formed for a lens system with a desired field angle of view, lensspeed and image quality. Especially for wide angles of view and highlens speed, it is preferred to use a multiple element back lens-groupwhereby a sharp image can be obtained.

In an embodiment, the multiple back lens group consists of four lenses,one of which is an achromate, and an aperture stop. The other lenses area condenser, a meniscus lens and a concave lens.

Suitable back lens groups forming sharp images can be designed by askilled person by using other lenses and other combinations thereof, andthey may be designed to include other functions e.g. a zoom.

The lenses are made of suitable materials that permit light of thedesired wavelengths to pass through. Wavelengths are generally in thevisible range of the electromagnetic spectrum, but wavelengths e.g. inthe infrared region are included. Suitable materials are known to askilled person. These materials comprise light transmissable materialsof glass, plastic, liquids. Glass or plastic of optical grade arepreferred.

Particularly, axial gradient index (GRIN) lenses may be used whereby asimplified construction or a higher quality image can be obtained.

One or more of the lenses can comprise a diffractive optical elementwhereby the back lens group can be even further simplified, the speedcan be increased or a higher image quality can be obtained.

Aspherical lenses can be used as well.

Correction of the various lens aberrations: spherical, coma,astigmatism, curvature of field and distortion can be done as for normallenses and objectives with the advantage that thick lenses, especiallyaxial gradient index lenses, and numerous lenses can be used without oralmost without increasing the effective lens height. Such an increase ofthe effective lens height depends on the folding angle between the frontlens group and the back lens group.

The back lens group may include one or more filters.

Reflective Element

According to the invention, the lens system comprises a reflectiveelement folding the first optical axis into the second optical axis inan angle a of less than 180 degrees whereby it is obtained that theoptical information (luminous flux) received by the front lens group istransformed to the back lens group so that an image can be formed on theimage recording device.

The reflective element can be any suitable reflective element known tothe skilled person, e.g. a prism or a mirror.

In a preferred embodiment, the reflective element consists of a flatfirst surface mirror whereby the luminous flux is reflected withouthaving to pass through a substrate.

The substrate for the flat first surface mirror should be chosen so thatit performs well with the reflective surface. It can be a rigid materialsuch as glass, particularly float glass, but other materials such asplastic or metals such as aluminium can be used. In a particularembodiment, the reflective element consists of an aluminium substratehaving a polished reflective surface.

In a preferred embodiment, the front lens group and the reflectiveelement consist of a prism.

Additional Reflective Element

In another preferred embodiment, the lens system comprises an additionalreflective element folding the second optical axis into the optical axisof the image recording device whereby a particular compact configurationof the lens system can be obtained.

The additional reflective element can be chosen as mentioned for thefirst reflective element.

In a preferred embodiment, the additional reflective element consists ofa prism.

Aperture Stop

The aperture stop of the lens system can be designed in any suitable wayknown to the skilled person. It is preferred that the aperture stop isdetermined by a stop placed after the first reflective element,particularly placed in the back lens group.

Folding and Orientations of Optical Axes

According to the invention, the lens system is a folded lens systemhaving the reflective element fold the first optical axis into thesecond optical axis in an angle a of less than 180 degrees whereby it isobtained that the lens system can be kept compact, particularly muchmore compact than that for non-folded lens systems of the prior art.

It is further obtained that relatively thick lenses can be used,especially in the back lens group whereby lenses of relativelynon-fragile dimensions can be used, e.g. gradient index lenses (GRINlenses), particularly axial GRIN lenses. Such lenses are available fromLightpath Technologies, Tuscon, Ariz., U.S.A.

Also, it is obtained that the back lens group may consist of severallenses whereby it is obtained that a better control of aberrations canbe achieved compared to a back lens group consisting of few lenses. Thisis important when designing a high speed lens system, typically a lenssystem with a front lens group having a large diameter.

In a preferred embodiment, the first optical axis and the second opticalaxis form an angle equal to or less than 90 degrees whereby aparticularly compact lens system can be obtained.

Also, in still another preferred embodiment, the second optical axis andthe optical axis of the image recording device form an angle equal to orless than 90 degrees whereby a still more compact lens system can beobtained depending on the extent of the image recording device. If theimage recording device is large, which is often the case, a more compactsystem is obtained.

The orientations of the optical axis can be designed for any suitablepurposes. In a preferred embodiment, the first optical axis and theoptical axis of the image recording device are substantially in the sameplane.

Further, it is preferred that the first optical axis and the opticalaxis of the image recording device are substantially parallel.

S-Ratio

A particularly preferred lens system has a ratio S of the optical systemheight H divided by the diameter D of the circumferential circle of theformed image less than 4, preferably equal to or less than 2.55, morepreferred equal to or less than 1.7, most preferred equal to or lessthan 1.2; said optical system height H being the maximum projecteddistance on the first optical axis from any part of the optical systemincluding lenses, filters, aperture stop, image recording device, andthe body thereof.

As it can be seen from the expression, a small S-ratio will provide acompact optical system.

A particularly preferred optical system has a ratio S of 2.55 or less,whereby it is obtained that the lens system can form an image of a sizeappropriate for e.g. a high resolution ¼″ CCD and the entire opticalsystem can be accommodated in the body of the image recording systemhaving a height b that conforms with the PCMCIA type III standard.

For a “heavy duty” embodiment with increased wall thickness and a largerparaxial image height for easier alignment, a ratio S of 2.1 or less ispreferred. Another preferred optical system has a ratio S of 1.7 orless, whereby it is obtained that the high resolution optical systemutilizing a ¼″ image recording device, e.g. a CCD, can be accommodatedin the body of the image recording system having a height b of about 7mm, which is desirable for keeping the image recording system in e.g. awallet or a small bag for carrying credit cards.

Still another preferred optical system has a ratio S of 1.2 or less,whereby it is obtained that the high resolution optical system utilizinga ¼″ image recording device, e.g. a CCD, can be accommodated in the bodyof the image recording system having a height b that conforms with thePCMCIA type II standard.

For a “heavy duty” embodiment with a better protection of the frontlens, an S-ratio of 1 or less is preferred.

The S-ratio is not limited to the applications as pointed out here.Where appropriate systems can be designed with an S-ratio suitable forthe application in question.

Height-ratio

It is particularly preferred that the height ratio of the effective lensheight h and the effective focal length f of the lens system are lessthan 1.7, preferably less than 1.5, whereby particularly compact, flatconfigurations as compared to prior art high resolution lens systems canbe obtained.

Receiving Optical Information Through a Broad Surface

According to the invention, the lens system receives the opticalinformation through one of the broad surfaces of the body of the opticalimage recording system whereby it is obtained that the viewfinder isproperly framed, i.e. it is easy to look through the viewfinder and seeonly the object to be imaged. As the height of the body can be very low,it is not appropriate to receive the optical information through a sideof the body.

For a system receiving the optical information from the side, stableplacement of the viewfinder in front of the eye would be difficult toachieve. Furthermore, for such a system, the viewfinder will take up alot of space.

Contrary to such a system, the optical image recording system accordingto the present invention will be very easy to hold still and to operate.No parts of it protrude from the user and it can be kept steady in oneor two hands thereby allowing operation thereof in an ergonomicallycorrect manner. For wall-mounted flat image recording systems, it is amust that the optical information is received through a broad surface.

Image Recording Device

According to the invention, the body accommodates an image recordingdevice having a light sensitive area. Image recording devices mayconsist of any suitable device which is able to record the opticalinformation formed into an image by the lens system in the form of asignal which can be processed in an image processing system.

It is preferred that the image recording device is a photosensitiveelectrical device, particularly a solid state image sensor such as acharge coupled device (CCD), a metallic oxide semiconductor (MOS), orsimilar.

When a solid state image sensor is used, the geometric distortion of thelens system can be electronically corrected whereby a large geometricdistortion of the lens system can be allowed. This has the advantagethat the front lens group can be made strongly refractive whereby thediameter of the last surface of the front lens group and the size of thefirst reflective element can be minimized, and consequently the heightof the lens system can be reduced.

The aspect ratio of the image recording device can be chosen within widelimits provided the radius of the active field of the image recordingdevice measured from the optical axis is within the real image height ofthe lens system. If the radius is larger, there will be “dead” pixelsnot being exposed to the formed image. Normally, an aspect ratio of 4/3is used for a solid state image sensor, but an aspect ratio of e.g. 16/9can also be used.

Optical Filter

The lens system may further comprise one or more optical filters which,according to the long back focus and folded lens system of theinvention, can be incorporated in the body without increasingthe-effective lens height.

In a preferred embodiment, the lens system comprises an anti-aliasingfilter inserted between the last lens in the back lens group and theimage recording device.

It is preferred that the anti-aliasing filter is a blur filter placedbetween the back lens group and the image recording device wherebyaliasing caused by the image recording device, e.g. a CCD, having acolour filter array on its surface and objects having a high degree ofdetails can be reduced.

The blur filter can be made as known in the art. It can consist of oneor more birefringent crystalline quartz plates having typically largethicknesses compared to the focal length of the optical system. Itsdesign depends on the structure of the pixels and the colour filterarray of the image recording device.

It is preferred that the filter has an optical axis parallel with thesecond optical axis of the optical system whereby it is obtained thatthe effective lens height can be kept small even if the filter is thickcompared to the focal length.

The filters may be placed in any suitable position. In a preferredembodiment, e.g. in the form of an electronic camera as described above,the filter is placed between the lens system and the image recordingdevice.

The filter can be several millimeters thick. However, if the filter isthick and positioned after the additional reflective element, it cannecessitate a large effective lens height.

If the filter is relatively thin e.g. consists of only few elements, orif the back focus is very long, it is obtained that an additionalreflective element can be inserted after the back lens group, preferablyafter the filter. Hereby it is further obtained that the second opticalaxis can be folded into the optical axis of the image recording devicewhereby image recording devices in standard housing can be used and theycan be mounted directly onto e.g. a printed circuit board.

The blur filter can be combined with an IR-blocking filter or otherfilters or combinations thereof.

For optical image recording systems where a blur filter is not needed,e.g. an optical image recording system with a fixed aperture stop and acolour filter array pattern allowing rotational symmetric blursgenerated by a defocusing of the lens system, the optical filter canconsist of one or more evaporated filters whereby it is obtained thatonly very little space is required in order to accommodate the filter.

In this case the optical filter can be evaporated on a lens surfacetaking due care that the spectral characteristics of the filter varywith the angle of incidence. To reduce this effect, it is preferred thatthe filter is placed so that the principal rays are normal to the filtersurface. In a preferred embodiment, an evaporated filter is applied tothe concave surface of the first lens.

When a birefringent blur filter is used it is necessary to correct theaberrations introduced by the filter. These corrections are known to theskilled person.

Body

According to the invention, the body can be any suitable body having aconfiguration with low height and with broad surfaces through one ofwhich surfaces the optical information is being received, which body canaccommodate the optical image recording system, and which body canprotect the optical image recording system both mechanically andoptically from the outside.

In a suitable embodiment, the body consists of a rigid construction witha thin wall of suitable material such as moulded plastic, die castedlight metal alloy or formed metal plate. The wall can also be of acomposite material such as carbon fibre reinforced plastic resin wherebya particularly preferred light and mechanically strong body is achieved.

Further, in order to protect the optical image recording system fromelectro-static discharge and to ensure electromagnetic compatibility,the body can be made of or can include a conductive material such ase.g. carbon fibres.

Generally, the height of the body is less than 20 mm whereby it isobtained that the body has a sufficiently flat configuration foraccommodation into slots of most commonly used dimensions in imageprocessing systems.

In a particularly preferred embodiment, the height is less than or equalto 10.5 mm whereby the body height conforms with the PCMCIA TYPE IIIstandard.

Most preferably the height is less than or equal to 5.0 mm, whereby thebody height conforms with the PCMCIA TYPE II standard.

For insertion into a wallet, a height of max 7 mm is desired.

Storing, Transferring and Receiving Electronic Signals

The body of the optical image recording system may further comprisevarious accessories for focussing, white balance control, automatic gaincontrol, etc. It may also contain a power supply, e.g. a battery.

In a preferred embodiment, the body further comprises means for storingelectronic signals of control information for controlling the operationof the external device.

In a particular embodiment, it is preferred that the body comprisesmeans for loading the control information into the external devicewhereby it is obtained that the operation of the external device, e.g.an image processing system not preset to process the optical images ofthe optical image recording system, can be controlled by the specificcontrol information loaded into the external device.

Control information includes system operation software such as softwarefor control of the image processing system and software for imageprocessing.

Transmission of the electronic signals may be carried out in anysuitable way known to the skilled person such as either by directconnection of the electric circuits of the optical image recordingsystem with that of the processing system, or by wirelesstransmission/reception.

When direct connection is applied, it is preferred that the guidance ofthe connection be controlled. Therefore, in a preferred embodiment, thebody further comprises guiding means for its guidance in a slot, grooveor the like.

It is not necessary that the body is inserted into the image proccesingsystem. In an embodiment, a display screen is connected onto the body ofthe optical image recording system. This connection may be permanent ornot, and the display screen may be integrally connected to the body.

Particularly, the embodiment of wireless transmission/reception has theadvantage of avoiding safety measures to ensure the guidance of theconnection of the optical image recording system and the processingsystem.

In a preferred embodiment, the means for transferring electronic signalscomprises a wireless transmitter of analogue and/or digitaltransmission.

Also, the means for receiving electronic signals comprise a wirelessreceiver of analogue and/or digital transmission.

Wireless transmitter and receiver can be any such suitable devices knownto the skilled person, e.g. radio transmitter/receiver or opticaltransmitter/receiver.

Optical Image Recording and Processing System

In another aspect, it is the object of the present invention to providean optical image recording and processing system for which opticalinformation can easily be tranferred from the optical image recordingsystem to an associated processing system.

This object is fulfilled according to the invention by providing anoptical image recording and processing system for the recording andprocessing of electrical signals of optical information and otherinformation; said system comprising means for transferring and receivingelec-tronic signals consisting of a pair of connector devices having adatabus interface, wherein one connector device of said pair ofconnector devices is accommodated in the optical image recording systemfor direct connection to the other of said pair of connector devicesaccommodated in the image processing system.

In a preferred embodiment, the connector device of the optical imagerecording system is accommodated in the end face thereof whereby aparticularly simple, connection with multiple connections can beestablished and a parallel databus for fast communication can beprovided. Furthermore, the connector device is well protected againstmechanical stress and it provides a good protection againstelectrostatic discharge (ESD)

In a preferred embodiment, the image processing system accommodates theconnector device in a slot whereby in a simple and safe way theaccommodation and connection of the optical image recording system isensured without having to use a cumbersome cable. The optical imagerecording system can be partly or fully inserted in the slot therebyensuring that sensitive parts, e.g. the lens system, are protectedagainst mechanical effects during connection with the image processingsystem.

Also, in a preferred embodiment, the optical image recording system andthe slot of the processing system comprise guiding means for guidingtheir mutual connection whereby a safe connection is ensured.

Particularly, it is preferred that the optical image recording andprocessing system comprises an optical image recording system accordingto the invention.

Suitable image processing systems are known in the art. They includecomputers such as personal computers and lab top computers; telephones,mobile phones, and satellite phones; fax machines; printers; displayscreens, and video tape units, but are not limited thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C show an optical image recording system according toprior art;

FIGS. 2A, 2B, 3A, 3B, 4, and 5 show cross-sectional views and a top viewof preferred optical image recording systems according to the presentinvention;

FIG. 6 shows a raytracing of the lens system according to a preferredembodiment of the present invention similar tp that shown in FIG. 2Awithout the filter 27;

FIG. 7 shows a spot diagram of the lens system of the preferredembodiment shown in FIG. 6;

FIG. 8 shows a polychromatic diffraction modulation transfer function(MTF) for the lens system of the preferred embodiment shown in FIG. 6;

FIG. 9 shows the field curvature (A) and geometrical distortion (B) ofthe lens system of the preferred embodiment shown in FIG. 6;

FIGS. 10A, 10B, and 10C show three views of a preferred embodiment of animage recording system according to the present invention;

FIG. 11 shows a preferred embodiment of the optical image recordingsystem non-inserted into an image processing system;

FIG. 12 shows the preferred embodiment shown in FIG. 11 inserted intothe image processing system also shown in FIG. 11;

FIGS. 13A and 13B show a cross-sectional view, of a preferred embodimentof the image recording system partly and completely inserted into animage processing system;

FIGS. 14A, 14B, 14C, and 14D show a preferred embodiment of the means ofguidance of the image recording system according to the presentinvention; and

FIG. 15 shows a block-diagramme of an embodiment of the image recordingsystem and its connection to an image processing system;

DETAILED DESCRIPTION

Prior Art

FIG. 1A shows a schematic top view of a broad surface of an opticalimage recording system according to prior art. The image recordingsystem includes a flat body 10 with broad surfaces; a lens system 11,said lens system being demountable as illustrated in FIGS. 1B and 1Cshowing end views from the line A-A; a two-dimensional image recordingdevice 12; and a connector device 13.

The optical information is received by and transformed into an image bythe lens system 11. The two-dimensional image recording device 12transforms the optical information into electrical information that canbe processed and stored in a semiconductor memory.

From the semiconductor memory the electrical information can betransferred to an image processing system through the connector device13.

In FIG. 1B, the effective lens height h, the optical system height H,and the body height b are shown.

In order to make the entire image recording system have a flatconfiguration, it is necessary to demount the lens system 11 asillustrated in FIG. 1C.

Preferred Embodiment According to the Invention

FIG. 2A shows a cross-sectional view and FIG. 2B shows a top view of apreferred embodiment of an optical image recording system according tothe present invention. It comprises a lens system comprising a frontlens group 21; a back lens group 22; a reflective element 23; anadditional reflective element 24; an aperture stop 26; and an optionalfilter 27. The optical image 28, having a circumferential circle of adiameter D, is formed by the lens system and transformed into electricalsignals by the image recording device 25.

The optical image recording system further comprises a body 20 withbroad surfaces 201 and 202 and a low height b, said body housing thelens system and the image recording device.

Contrary to FIG. 1, prior art, the lens system is accommodated in thebody 20, whereby the optical image recording system at all times has alow height b and a robust structure. The optical system height H as wellas the effective lens height h is smaller than the body height b.

The optical information is received through the front lens group 21having the optical axis 211 and is then reflected by the reflectiveelement 23 in an angle a into the optical axis 221 of the back lensgroup 22. The additional reflective element 24 reflects the unfocusedimage onto the light sensitive surface of the image recording device 25having an optical axis 251.

In the preferred embodiment, the semifield angle of view is 33 degrees—arelatively wide field. In order to provide enough space for thereflective element 23 between the front lens group 21 and the back lensgroup 22, an inverted telephoto principle is chosen. The invertedtelephoto principle further has the advantage that it provides a goodstandard of uniformity of image illumination and definition. Also, itprovides space for optical filters.

The front lens group 21 is made out of one lens only, said lens beingstrongly dispersive. By having only one lens in the front lens group 21and by letting said lens being strongly dispersive, the height of thefront lens group and diameter of the last surface of the front lensgroup 21 is minized. Thereby, the height of the reflective element 23 isminimized and consequently the height H of the optical system and theheight b of the body 20 is minimized.

In the preferred embodiment the first lens in the front lens group 21 ismade out of BAK50 which is a hard stratch-resistant glass type with goodchemical and climatic resistance.

Other glass types or for instance plastic can be used for the lenssystem, but it should be recognized that this might have an influence onthe performance. All the prescribed glass types used in the preferredembodiment of the present invention are available at Schott Glaswerke,Hatterbergstrasse 10, D-6500 Mainz, Germany.

The back lens group 22 is a collective member made out of four elements,one of which is an achromate. As the optical information received by thefront lens group 21 is reflected in an angle a of less than 180 degreesby the reflective element 23, the length of the back lens group 22 doesnot, or only slightly, influence the height b of the body 20. Hence, itis possible to have a plurality of lenses in the back lens group 22 anda large relative aperture and obtain a good sharp image. Furthermore, itis possible to make use of relatively thick lenses and achromates likefor example the first lens and the achromate in the back lens group 22.

The data of the lens system of the preferred embodiment of the presentinvention shown in FIG. 6 are shown in Table 1.

TABLE 1 Surface Radius Thickness Glass Diameter Object Infinity 10311268.761  1 69.82798 0.62491 BAK50 5.5685  2 3.08561 2.79169 4.4154  3coordbrk 0 0  4 Infinity 0 Mirror 5.3371  5 coordbrk −2.79169 0  6−14.03706 −2.20607 BAFN6 3.7858  7 5.85567 −0.27864 3.5009  8 −2.89064−0.67185 BALF5 2.8786  9 −20.0553 −0.05665 2.6079 10 Stop Infinity−0.17353 2.5891 11 16.94942 −0.62243 F6 2.5588 12 −2.89336 −0.196912.4885 13 −9.22677 −1.10781 SF4 2.4885 14 −2.99430 −0.77470 LAKN7 2.670815 7.23099 −3.65 2.8492 16 0 0 coordbrk 17 Infinity 0 Mirror 5.1239 181.95296 0 coordbrk Image Infinity 0 4.6059 Units: mm Effective focallength f: 3.98 Aperture: F#2.8

The lens system has an S-ratio of 1.2 making it ideal for a “heavy duty”“wallet camera”, and through about 13% down scaling it is ideal for animage recording system with a body having a height b that conforms withthe PCMCIA type II standard.

A skilled person can select the data and materials of the various lenselements and other components suitable for alternative designs,considering changes in performances.

The reflective elements 23 and 24 are in the preferred embodiment firstsurface mirrors. They can be replaced by prisms.

In an embodiment with SLR (Single Lens Reflex) function the additionalreflective element can be replaced by a beam splitter, dividing theimage 28 formed by the lens system into two images: one focusing on theimage recording device 25, the other being transformed into a viewer asit is known in the art. In this way a zoom function can be establishedin a very flat design.

In the preferred embodiment of the present invention, the imagerecording device 25 is a two-dimensional array CCD (Charge CoupledDevice) image sensor. The optical image 28 formed by the lens system istransformed into electrical signals by the image recording device 25.These electrical signals can be processed and stored on a data storingdevice, typically a semiconductor memory.

FIGS. 3A and 3B show the lens system and optical image recording device25 in an embodiment with a non-rotary-symmetrical front lens groupelement and a decreased angle a. As the active part of the imagerecording device in the preferred embodiment is rectangular, lenses farfrom the aperture stop 26 do not need to be rotary-symmetrical. In FIG.3A this feature is used to decrease the angle a, whereby it is obtainedthat the effective lens height h of the lens system can be decreased, orthat the length of the optical axis 251 from the reflective element 24to the image recording device 25 can be increased without increasing theeffective lens height h. This is important when utilizing a CCD (orother type of optical image recording device) in a housing 31 with wallsbeing in a higher level than the active part of the CCD. This isillustrated in FIG. 3A. By making the effective lens height hconsiderably smaller than the total height H of the optical system, itis possible to mount the CCD 25 directly on a printed circuit board 32,whereby the electronical part of the optical image recording system canbe simplified and made more compact, since only one printed circuitboard is required. Further, according to the general principle of “chipson board” technology, components 33 may be positioned on both sides ofthe printed circuit board 32 without increasing the total height H ofthe optical system and thereby the height b of the optical imagerecording system. This is illustrated in FIG. 3B.

FIG. 4 shows the lens system and image recording device in an embodimentwith a U-shaped optical path from the front lens group 21 to the imagerecording device 25. As in FIGS. 2 and 3 the optical informationreceived by the front lens group 21 is reflected to the back lens group22 by the reflective element 23. The image formed by the lens system isthen reflected by the reflective element 24 to the image recordingdevice 25.

The embodiment shown in FIG. 4 is especially useful in applicationswhere the effective lens height h must be very small, and inapplications with more than one lens in the front lens group 21.

When the length of the optical axis 211 from the front point of thefirst optical element having the optical axis 211 as its optical axis tothe reflective element 23 is relatively long (due to a large front lensgroup), the embodiment shown in FIG. 4 can be used in order to minimizethe total height H or in order to make it possible to utilize a CCD in astandard housing. Furthermore, a filter, e.g. a blur filter, can beinserted between the reflective element 24 and the image recordingdevice 25.

FIG. 5 shows the lens system and image recording device 25 in anembodiment with only one reflective element 23. In this embodiment ofthe present invention the second reflective element 24 has been leftout, whereby the number of components is reduced and the lens system issimplified.

This preferred embodiment of the present invention allows the imagerecording device 25 to be thick in the direction of the optical axis221. For applications where a good cooling of the image recording device25 is desirable, e.g. under low-light conditions requiring a largesignal-to-noise ratio, the embodiment shown in FIG. 5 can be used. Itprovides space on the back of the image recording device 25 forarrangements of one or more cooling devices such as e.g. heat sinks,cooling fans or peltier elements. Because of the long back focus and theomission of the second reflective element 24, the embodiment furtherprovides space for optical filters 27 of a considerable thicknessbetween the last lens in the back lens group 22 and the optical imagerecording device 25. Depending on the image recording device 25, abirefringent blur filter will usually provide a better image quality.This embodiment of the present invention provides space for a multipleplate birefringent blur filter for improved image quality. Due to achoice of the folding angle a, the distance in the direction of theoptical axis 211 from the outer surface 201 of the body 20 to the centerof the image recording device 25 can be chosen to be close to half thebody height b of the body 20. In this way the image recording device 25can utilize the total available height inside the body 20 and hence thesize of the image recording device 25 can be maximized, whereby optimumresolution and sensitivity is ensured.

FIG. 6 shows a raytracing of the lens system according to a preferredembodiment of the present invention. The raytracing is shown with theoptical axis 211, 221 and 251 in the paper plane and an aperture F#:2.8.

FIG. 7 shows a spot diagram of the lens system of the preferredembodiment shown in FIG. 6. Four fields are shown: A, B, C and D. Thedata for the four fields are as shown in Table 2.

TABLE 2 Field A B C D Object 0.00 13.09 26.18 −26.18 (deg.) 0.00 10.0620.12 −20.12 Image (mm) 0.00 0.90 1.76 −1.76 0.00 0.69 1.31 −1.31 RMSradius 1.268 1.815 1.462 1.454 (micron) Geometrical 2.934 4.676 5.1824.066 radius (micron) Reference: Chief ray. The length L of the scalebar is 20 micron.

The RMS radius is the root mean square radius of the spot. Nodiffraction is considered in these calculations. The analysis has beenmade by using the optical design program Zemax v.2.8 and v.4.0 fromFocus Software Inc., P.O.Box 18228, Tucson, Ariz. 85731, USA.

FIG. 8 shows a polychromatic diffraction modulation transfer function(MTF) for the lens system of the preferred embodiment shown in FIG. 6and at full aperture. The MTF is shown for four fields: A, B, C and D.The fields are the same as in FIG. 7. DL is the diffraction limit. TheY-axis is the contrast of an image of a sinusoidal grating object. TheX-axis is the spatial frequency in cycles per millimeter in the imagedgrating.

FIG. 9 shows the field curvature (A) and geometrical distortion (B) ofthe lens system of the preferred embodiment shown in FIG. 6. The fieldcurvature plot shows the distance from the actual image plane to theparaxial image plane as a function of the field angle. The X-axis is thefield curvature in millimeters. Full Y-axis equals 63 degree full fieldof view. Tangential (T) and Sagittal (S) focal lines are shown for threedifferent wavelengths: 0.486 microns, 0.588 microns and 0.656 microns.

For the geometrical distortion a full Y-axis equals 63 degree full fieldof view. The units on the X-axis is in percent.

FIGS. 10A, 10B, and 10C show three views of a preferred embodiment of animage recording system according to the present invention. In thispreferred embodiment the body 20 is card-shaped, whereby it can be keptin a wallet or a small handbag for carrying credit cards. Furthermore itcomprises a connector device 1001 having connector pins 1003, and thebody 20 is provided with means of guidance 1004, whereby it is possibleto insert and connect the optical image recording system in the slot ofan image processing system. The optical information is received andformed into an image by the lens system as described for the embodimentshown in FIGS. 2A and 2B. The image recording device 25 transforms theoptical information into electrical information which is stored in thesolid state memory 1002. In the preferred embodiment this memory isdemountable and replaceable. The solid state memory is a flash memory asit is known in the art. Other kinds of memory devices can be used aswell. The broad surfaces 201 and 202 makes it possible to use one ormore PCB's (Printed Circuit Boards) for the mounting of the electronicalcircuits and components necessary for controlling the image recordingdevice 25 and for processing the electrical information from the imagerecording device 25. Furthermore, the broad surfaces 201 and 202 make itpossible to provide the optical image recording system with an effectiveand “easy to use” viewer 1006 for pointing out the object to berecorded. The optical image recording system also comprises a shutter1007 for activating the image recording system. By the use ofpolarization keys 1005 it is obtained that the image recording system isnot reversed when inserted into an image processing system. Thepolarization keys also make it possible to ensure that the imagerecording system can only be inserted into image processing systems andchargers having the correct voltage and pin configuration. The means ofguidance 1004 helps inserting the image recording system in the matingimage processing system, charger or the like. It also means that thebody 20 can have many various designs, sizes and shapes and can stilleasily be inserted into the mating unit. In this way it is possible toadd or subtract features and obtain a flexible design platform withinthe same “frame” provided by the means of guidance 1004. The connectorpins 1003 of the connector device 1001 are housed inside the connectordevice 1001. They are hereby protected from mechanical and electricalstress such as electro-static discharge that can otherwise damage thesensible electronics inside the optical image recording system.

FIG. 11 shows the optical image recording system 1000 non-inserted intothe image processing system 1100. The means of guidance 1004 (thehatched parts) of the image recording system 1000 mates the means ofguidance 1101 of the image processing system 1100 and ensures a safe andeasy connection of the two systems.

FIG. 12 shows the optical image recording system 1000 inserted into theimage processing system 1100. When the two systems are connected, theyappear in the preferred embodiment of the present invention as onesingle unit.

FIGS. 13A and 13B show a cross-sectional view of a preferred embodimentof the image recording device 1000 partly and completely inserted intothe image processing system 1100. The image processing system 1100comprises a connector 1301 and polarization keys 1302 mating theconnector 1001 and the polarization keys 1005 of the image recordingsystem 1000.

FIGS. 14A, 14B, 14C, and 14D show a preferred embodiment of the means ofguidance 1004 of the image recording system according to the presentinvention. The hatched parts on the body 20 are the preferred embodimentof the means of guidance 1004. It stretches all along the side of thebody 20 whereby a good guidance in the total length of the body 20 ofthe image recording system is obtained. Furthermore, especially aroundthe connector device 1001, a good guidance is obtained. In this way itis possible in the preferred embodiment to utilize small and fragileconnector pins in the connector devices 1001 and 1301. Hence a largenumber of connector pins can be used and a fast parallel data bus can beformed.

FIG. 15 shows a block-diagram of an embodiment of the image recordingdevice and its connection to an image processing system. The opticalinformation is received through the lens 1501 and formed into an imagerecorded by the image recording device 25. The electrical information isthen passed on to a CCD drive section 1502 and a signal processingsection 1503, as it is known in the art. The output signal istransformed to digital form via an A/D (Analog/Digital) converter 1504.The databus 1505 exchanges information between each section of the imagerecording system. Image processing software for the image processingsystem 1100 is stored in the memory 1506 and can be transferred to theimage processing system 1100 when the image recording system 1000 isconnected thereto either by wire or wireless. In this way it is obtainedthat data from the image recording system can be processed on any imageprocessing system, provided the image processing system comprises amating connector device and/or a receiver/transmitter device and anoperating system capable of operating the software provided by the imagerecording system.

Further, signal processing and correction of geometrical distortionintroduced by the lens system 1501 can be done in the processing block1508, whereafter the data are compressed in the data compressor 1509.The data can then be stored in the memory 1002. An optional buffermemory 1507 ensures that data from the A/D converter 1504 can betemporarily stored before they are processed in 1508 and data compressedin 1509.

Data stored in the memory 1002 can be transferred to the imageprocessing system 1100 via the databus controller 1505 and the connectordevices 1001 and 1301. The data are processed in the image and dataprocessing device 1510.

Hence processing including correction of geometrical distortion does nothave to take place in the image recording system 1000, but can very wellbe done in the image processing system 1100.

The structure of the image recording system and the image processingsystem can be altered and designed differently from what is known in theart, just as a beam-splitting prism can be inserted between the lens1501 and the image recording device 25, whereby three separate imagers R(Red), G (Green) and B (Blue) can be used.

1. A lens system comprising: a front lens group having a first opticalaxis; a back lens group having a second optical axis, wherein a lens inthe back lens group, which is closest to the front lens group, ispositioned at the cut off portion of front lens group, wherein the firstoptical axis is substantially parallel with a height direction of thelens system, wherein the second optical axis is substantially parallelwith a length direction of the lens system so that a plurality of lensesare included in the back lens group without increasing the height of thelens system, and wherein the back lens group includes an aperture stophaving surface substantially perpendicular with the second optical axis;a reflective element folding said first optical axis into said secondoptical axis in an angle of less than 180 degrees; wherein at least onelens adjacent to said reflective element is a non-rotary symmetricallens.
 2. The system according to claim 1, wherein the lens systemcomprises an additional reflective element folding the second opticalaxis into an optical axis of an image recording device.
 3. The systemaccording to claim 1, wherein the first optical axis and the secondoptical axis form an angle equal to or less than 90 degrees.
 4. Thesystem according to claim 1, wherein the second optical axis and anoptical axis of an image recording device form an angle equal to or lessthan 90 degrees.
 5. The system according to claim 1, wherein an imagerecording device is a charge coupled device.
 6. The system according toclaim 1, wherein the lens system has a ratio of an optical system heightdivided by a diameter of a circumferential circle of a formed image lessthan
 4. 7. The system according to claim 1, wherein a height ratio of aneffective lens height and an effective focal length of the lens systemis less than 1.7.
 8. The system according to claim 1, wherein a heightof a body is less than 20 mm.
 9. The system according to claim 1,wherein the front lens group and the reflective element consist of aprism.
 10. The system according to claim 1, wherein an additionalreflective element consist of a prism.
 11. The system according to claim1, further comprising a body further comprising means for storing,transferring and receiving electronic signals of optical information andother information to and from an external device.
 12. The systemaccording to claim 11, wherein the means for transferring and receivingelectronic signals comprise a connector device having a databusinterface.
 13. The system according to claim 12, wherein the connectordevice is accommodated in an end face of said body.
 14. The systemaccording to claim 11, wherein the storage means for storing theelectronic signals consist of an exchangeable memory.
 15. The systemaccording to claim 11, wherein the means for transferring electronicsignals comprise a wireless transmitter of analogue and/or digitaltransmission.
 16. The system according to claim 11, wherein the meansfor receiving electronic signals comprises a wireless receiver of analogand/or digital transmission.
 17. The system according to claim 1,wherein a body further comprises means for storing electronic signals ofcontrol information for controlling the operation of an external device.18. The system according to claim 17, which comprises means for loadingthe control information into the external device.
 19. The systemaccording to claim 1, wherein a body further comprises guiding means.20. An optical image recording system for electric recording of opticalinformation, the optical image recording system comprising: a lenssystem and a body; and wherein the lens system comprises: a front lensgroup having a first optical axis; a back lens group having a secondoptical axis, wherein a lens in the back lens group, which is closest tothe front lens group, is positioned at the cut off portion of front lensgroup, wherein the first optical axis is substantially parallel with aheight direction of the lens system, wherein the second optical axis issubstantially parallel with a length direction of the lens system sothat a plurality of lenses are included in the back lens group withoutincreasing the height of the lens system, and wherein the back lensgroup includes an aperture stop having surface substantiallyperpendicular with the second optical axis; a reflective element foldingsaid first optical axis into said second optical axis in an angle ofless than 180 degrees; wherein at least one lens adjacent to saidreflective element is a non-rotary symmetrical lens.
 21. The systemaccording to claim 20, wherein the lens system comprises an additionalreflective element folding the second optical axis into the optical axisof an image recording device.
 22. The system according to claim 21,wherein said body further comprises guiding means.
 23. The systemaccording to claim 20, wherein the first optical axis and the secondoptical axis form an angle equal to or less than 90 degrees.
 24. Thesystem according to claim 20, wherein the second optical axis and anoptical axis of an image recording device form an angle equal to or lessthan 90 degrees.
 25. The system according to claim 20, wherein an imagerecording device is a charge coupled device.
 26. The system according toclaim 20, wherein the lens system has a ratio of an optical systemheight divided by the diameter of the circumferential circle of theformed image less than
 4. 27. The system according to claim 20, whereina height ratio of the effective lens height and the effective focallength of the lens system is less than 1.7.
 28. The system according toclaim 20, wherein the height of said body is less than 20 mm.
 29. Thesystem according to claim 20, wherein the front lens group and thereflective element consist of a prism.
 30. The system according to claim20, wherein an additional reflective element consists of a prism. 31.The system according to claim 20, wherein said body further comprisesmeans for storing, transferring and receiving electronic signals ofoptical information and other information to and from an externaldevice.
 32. The system according to claim 31, wherein the means forreceiving electronic signals comprises a wireless receiver of analogand/or digital transmission.
 33. The system according to claim 31,wherein the means for transferring electronic signals comprise awireless transmitter of analogue and/or digital transmission.
 34. Thesystem according to claim 31, wherein the storage means for storing theelectronic signals consist of an exchangeable memory.
 35. The systemaccording to claim 31, wherein the means for transferring and receivingelectronic signals comprise a connector device having a databusinterface.
 36. The system according to claim 35, wherein the connectordevice is accommodated in an end face of said body.
 37. The systemaccording to claim 20, wherein the body further comprises means forstoring electronic signals of control information for controlling theoperation of the external device.
 38. The system according to claim 37,which further comprises means for loading the control information intothe external device.